A secondary battery such as a lithium-ion secondary cell is generally provided in the form of a battery pack having a battery cell and a protective circuit integrated with each other, so as to safely secure cooperation between the battery cell and an outside load or a battery charger to be connected to the battery cell.
The protective circuit is provided with a cutoff switch such as a relay for cutting off a power path connecting the battery cell and the outside load in case of an emergency. When the protective circuit detects abnormality such as overcharge, it immediately actuates the cutoff switch to thus cut off the power path, thereby protecting the battery cell and the outside load or the like (see, for example, paragraph [0002] in JP-A-2010-140785).
When a battery pack having a high output is used in outdoor environment as a power supply for an electric vehicle (EV), a power supply for home, or industrial power supply, malfunction may be caused. Furthermore, there is a difficulty in detecting abnormality with high stability. Thus, there is a demand for further improving the reliability of the protective circuit.